When Google added Instant Previews to user search results, there were questions as to how and when the images were created:



Google have now added an additional feature to the popular Webmaster Tools (under Labs) to help website owners find issues which may be affecting the preview image generated by Google.

The tool gives you the option to specify any web page on your site and then generates a preview on the spot.   It compares the preview to the actual site side by side:




As you can see above, there are some small discrepancies (some borders/menu elements are missing), however this appears to be fairly random?  

Repeatedly hitting the compare button gives different results – possibly indicating a bandwidth issue when downloading pictures?   Maybe because so many webmasters are hitting the new tool at the moment!

Below the comparison, the tool provides a list of errors encountered when processing the site.    In the above example, the missing bitmaps are listed as “fetch failure”, which is odd as the images download fine for normal browsers.

This also raises the question – if the image on the left of the actual site is also generated in real time for the comparison – how come it succeeds to download all the pictures, whereas the instant preview doesn’t?

Google states that the image preview is generated using a WebKit engine which doesn’t support flash or Silverlight which may account for differences between the real site and the preview.


Check out the Google webmaster central blog for the official Google announcement.